The present invention relates to a timing transmission device for an internal combustion engine, and more particularly, to an improved form of timing transmission device in which a crankshaft is rotatably supported on an engine body and a drive gear and a driven gear are fixedly provided on the camshaft, the drive and driven gears being operatively connected to each other through the intermediary of an idler gear.
In such timing transmission devices of the prior art, an idler gear is rotatably mounted on the engine body by a bolt, for example, as described in Japanese Utility Model Publication No. 59-10321 (No. 10321/1984) Generally, during driving a vehicle employing an engine of this type, the amount of thermal expansion incurred by the engine body is greater than that incurred by the timing transmission device. This results from differences in material used for the engine body and the timing transmission device, respectively, as they are acted upon by heat transmitted from a combustion chamber. For this reason, according to the prior art construction mentioned above, the thermal expansion of the engine body tends to increase the distance between the shafts of the drive gear and the idler gear, thereby to create a backlash of significant magnitude between the gears. This results in undesirable meshing noise accompanying the meshing of the respective gears.
In light of such circumstance, it is an object of the present invention to provide a timing transmission device which maintains an appropriate condition of meshing between the drive gear and the idler gear and which is capable of quiet operation, notwithstanding the affects of the thermal expansion of the engine body.